It is well known that articles of trade and commerce whose value depends upon authenticity are subject to counterfeit. Such articles include currency such as coins and banknotes, and investment commodities such as bullion coins and bars, but may also include luxury items such as designer apparel and accessories. In some cases, such as banknotes, substantially all of the value of the article may derive from its authenticity, that is the confidence that it is what it appears to be which may concern its materials, utility, or its source or conditions of manufacture.
Many methods and techniques have been developed to enable authentication of valuable articles and are generally directed to enabling a person to distinguish between authentic articles and counterfeit articles. In some cases, authentication undesirably requires alteration to the article being authenticated. For example, gold coins and gold wafers are an investment means which people buy either to invest or to save. Gold can be determined as real gold through traditional methods such as chemical assays, instrumental analysis assays, fire assays, stone assays, and so forth. All of these methods are destructive, however, and require equipment, expertise, know-how, experience, and time. In addition, the authentication services may not be easily accessible to the public where and when needed.
Alternatively, some methods do not require alteration of the article, but instead rely upon preexisting physicochemical characteristics of the article which may be measured and used to generate an identifier associated with the article and which is subsequently used in its remote authentication. For example, World Intellectual Property Organization International Publication Number WO 2012/145842 by the present inventors, and which is incorporated herein in its entirety, discloses a method wherein an image of an article, specifically a coin, is captured and a digital representation of an acquisition area of the coin including a feature is generated. The feature may include a first component common to more than one coin and a second component unique to the coin. The feature may be random, such as naturally occurring features resulting from handling or processing during manufacture, or may be deterministic such as an intentionally applied feature produced by known fabrication techniques. An identifier is generated based on the digital representation of the feature and is later used to authenticate the coin.
The above method suffers the disadvantage, however, that for certain materials such as dense metals like gold, the random, naturally occurring features are relatively fine-grained and not distinguishable at low magnification, e.g. about 20 times. Producing digital representations of such naturally occurring features in such a case which are sufficiently reliable for the purposes of authentication thus requires relatively expensive equipment which is not typically available to a wide variety of users. Accordingly, the method may not permit convenient implementation for such materials using inexpensive, ubiquitous equipment available to a wide variety of users.
While the above solutions enable a high level of security including authentication, further improvements are possible and desirable. In particular, it is desirable to provide a method which renders as difficult as possible any forgery or false authentication by a counterfeiter, but at the same time enables quick and reliable authentication without need for special expertise or equipment.